Worst mass shootings in U.S. – Police officers walk on a rooftop at the Washington Navy Yard on Monday, September 16, after a shooting rampage in the nation's capital. At least 12 people and suspect Aaron Alexis were killed, according to authorities.

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Worst mass shootings in U.S. – Connecticut State Police evacuate children from Sandy Hook Elementary School in Newtown, Connecticut, on December 14, 2012. Adam Lanza opened fire in the school, killing 20 children and six adults before killing himself. Police say he also shot and killed his mother in her Newtown home.

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Worst mass shootings in U.S. – James Holmes pleaded not guilty by reason of insanity to opening fire July 20, 2012, at the Century Aurora 16 theater in Aurora, Colorado, during the midnight premiere of "The Dark Knight Rises." Twelve people were killed and dozens were wounded. Holmes is charged with 142 counts, including first-degree murder. His trial is scheduled to begin in February 2014.

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Worst mass shootings in U.S. – A military jury convicted Army Maj. Nidal Hasan on Friday, August 23, 2013, of 13 counts of premeditated murder in a shooting rampage at Fort Hood, Texas. During the November 5, 2009 shooting, 13 people died and 32 were injured.

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Worst mass shootings in U.S. – Jiverly Wong shot and killed 13 people at the American Civic Association in Binghamton, New York, before turning the gun on himself on April 3, 2009, police say. Four other people were injured at the immigration center shooting. Wong had been taking English classes at the center.

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Worst mass shootings in U.S. – Pallbearers carry a casket of one of Michael McLendon's 10 victims. McLendon shot and killed his mother in her Kingston, Alabama, home, before shooting his aunt, uncle, grandparents and five more people. He shot and killed himself in Samson, Alabama, on March 10, 2009. McClendon left a note saying he put his mother "out of her misery."

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Worst mass shootings in U.S. – Virginia Tech student Seung-Hui Cho went on a shooting spree on the campus in Blacksburg, Virginia, on April 16, 2007. Cho killed two people at the West Ambler Johnston dormitory and, after chaining the doors closed, killed another 30 at Norris Hall, home to the Engineering Science and Mechanics Department. He wounded 17 people before killing himself. It is the deadliest shooting rampage in U.S. history.

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Worst mass shootings in U.S. – Mark Barton walked into two Atlanta trading firms on July 29, 1999, and fired shots, leaving nine dead and 13 wounded, police say. Hours later police found Barton at a gas station in Acworth, Georgia, where he pulled a gun and killed himself. The day before Barton had bludgeoned his wife and his two children in their Stockbridge, Georgia, apartment, police say. The children's birth mother and grandmother had been murdered six years earlier in Alabama. Barton was questioned but never charged in that crime.

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Worst mass shootings in U.S. – Eric Harris, left, and Dylan Klebold entered Columbine High School in Littleton, Colorado, on April 20, 1999, armed with bombs and guns. The students killed 13 and wounded 23 before killing themselves.

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Worst mass shootings in U.S. – George Hennard crashed his pickup through the plate glass window of Luby's Cafeteria in Killeen, Texas, on October 16, 1991, before fatally shooting 23 people and committing suicide.

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Worst mass shootings in U.S. – James Huberty shot and killed 21 people, including children, at a McDonald's in San Ysidro, California, on July 18, 1984. A police sharpshooter killed Huberty an hour after the rampage began.

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Worst mass shootings in U.S. – Prison guard George Banks is led through the Luzerne County courthouse in 1985. Banks killed 13 people, including five of his children, in Wilkes-Barre, Pennsylvania, on September 25, 1982. He was sentenced to death in 1993 and received a stay of execution in 2004. His death sentence was overturned in 2010.

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Worst mass shootings in U.S. – Officers carry victims across the University of Texas at Austin campus after Charles Joseph Whitman opened fire from the school's tower, killing 16 people and wounding 30. Police officers shot and killed Whitman, who had killed his mother and wife earlier in the day.

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Worst mass shootings in U.S. – Howard Unruh, a World War II veteran, shot and killed 13 of his neighbors on September 5, 1949, In Camden, New Jersey. Unruh barricaded himself in his house after the shooting. Police overpowered him the next day. He was ruled criminally insane and committed to a state mental institution.

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Story highlights

Crime rates have been declining for years

Most crimes are committed by people known to the victims

But perception of crime doesn't always match statistics

Many U.S. residents believe crime is getting worse

You can't escape the headlines. An Australian going to college in the United States is gunned down by teens who police say killed him out of boredom. A few days later, a World War II veteran is beaten to death for reasons still unknown.

The death of Australian Christopher Lane in Duncan, Oklahoma, even sparked calls for Aussies to boycott travel to the United States because of all the violence.

Two shocking, high-profile crimes, one question: "What the hell is going on!?" Facebook user Stacey James Gordon wrote on CNN's Facebook page.

Although the cases have struck a nerve with their disturbing randomness and apparent cruelty, the reality is that living in the United States may never have been safer, and you're much more likely to be the victim of a crime committed by someone you know than you are to be assaulted by a stranger.

Nearly eight of every 10 murders in the United States between 1993 and 2008 were committed by someone the victim knew, according a 2010 report by the federal Bureau of Justice Statistics. The report didn't include figures for 2011 or 2012.

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WWII veteran beaten to death

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Thrill kill in Oklahoma

Similarly, nearly two out of every three nonviolent crimes were committed by someone the victim knew.

Pair that with figures on overall crime: According to the FBI, the violent crime rate in the United States is about half what it was in 1992.

And between 1992 and 2011, the annual number of murders in the United States fell from 23,760 to 14,612 despite a growing population.

Rape, robbery, assault, even property crimes also fell in a well-documented decline that has gone on for years, albeit with a small upturn in 2012.

Criminologists have cited shifts in the crack cocaine market, which drove many 1990s-era murders; an increase in the number of offenders behind bars; the country's aging population; and more sophisticated policing for the declines.

But perceptions of crime haven't always followed the reality.

In May, a Pew Research Center study found that 56% of Americans believe that gun violence is higher than it was 20 year ago, even though it has fallen precipitously since the 1990s.

And in 2011, Gallup found that 68% of Americans believed crime was getting worse, despite the reality of declining crime rates nationwide.